This invention relates to image reproduction, and in particular to reproduction methods and apparatus based on input scanning.
In the field of image reproduction, methods and apparatus are used to produce images which can be acquired from a variety of digital input devices (e.g., various types of digital cameras and scanners) and displayed on a variety of output devices (e.g., various types of hardcopy and softcopy output devices). The necessary input device resolution is determined based upon the input device modulation transfer function (MTF), the output device MTF, the user""s desired amount of zoom/crop, the display medium, and perceived image quality and acceptability.
Recently, there has been great interest in the optimal scan resolution for digital imaging systems. Previous research suggests that image resolution affects perceived image quality (J. H. D. M. Westerink and J. A. J. Roufs, xe2x80x9cA Local Basis for Perceptually Relevant Resolution Measuresxe2x80x9d, SID 88 Digest, pp. 360-363, (1988), and J. H. D. M. Westerink and J. A. J. Roufs, xe2x80x9cSubjective Image Quality as a Function of Viewing Distance, Resolution, and Picture Sizexe2x80x9d, SMPTE Journal, pp. 113-119, February 1989). However, these studies do not provide data for many other important variables that may alter perceived image quality due to resolution, particularly zoom/crop amount, for various film scanner resolutions.
Currently, the scan resolution for imaging systems has been based on methods that evaluate the system processing speed, size of the image buffer, and the developer""s judgment of image quality. These methods do not take into account the typical user""s perception of image quality. In designing a system that provides the best trade-off between image quality and system processing speed and the size of the image buffer, it would be desirable to determine an optimal resolution. However, the methods described to date do not determine the necessary resolution for the specification of an imaging system as a function of empirically derived image quality data and system requirements. Consequently, a user requesting a desired zoom/crop amount from an imaging system, e.g., a database of images accessible over the internet, may obtain degraded image quality due to insufficient scan resolution.
Consequently, besides providing specifications for film digitization systems, knowledge of a minimally necessary scan resolution could provide the basis for warning a user when there is inadequate scan resolution for a desired zoom/crop amount at a particular image quality level.
It is an object of the invention to determine the necessary scan resolution for users to zoom and crop images by various amounts.
It is a further object of the invention to determine the necessary resolution for the specification of an imaging system as a function of empirically derived image quality data and system requirements.
It is a further object of the invention to provide a warning to a user when there is inadequate scan resolution for a desired zoom/crop amount and image quality level.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention uses empirically derived image quality data in order to determine an image resolution for a particular zoom and/or crop operation performed on an image. An acceptability value is specified for the image, e.g., a specific % acceptable, where the acceptability value relates to empirically derived image quality as perceived by a human viewer. Given a selected output medium, an image resolution is then generated from a combination of the particular zoom and crop, the specified acceptability value and the selected output medium. This resolution is specified as the image resolution, e.g., a minimally acceptable resolution, to produce the desired zoom and crop.
Approached from a different aspect, the invention also resides in a method for warning a user of inadequate scan resolution to zoom and/or crop an image at an acceptable image quality. The user indicates a desire to perform a given zoom and crop operation on the image for a preferred display medium. A minimally acceptable scan resolution for the desired amount of zoom and crop is generated by relating the specified acceptability value to the desired zoom and crop and the preferred display medium. This determines the resolution of the digital image necessary to produce the desired zoom and crop. If the desired zoom and crop will be provided at less than the minimally acceptable scan resolution, then a warning will be provided to the user.
From yet another aspect, the invention resides in determining the acceptability of an image by starting with an objective metric related to sharpness, such as image acutance. The invention, from this aspect, involves relating a particular zoom and crop imaging operation to the objective sharpness metric and then relating the objective sharpness metric to a subjective acceptability metric that is based upon evaluation of particular images modified by application of the particular imaging operation. The acceptability metric is then compared to an acceptability threshold to determine the acceptability of an image that is selected for the particular imaging operation.
The advantage of the method described above resides in its novel means for using empirically derived image quality data to provide a warning to the user of degraded image quality due to insufficient scan resolution. Moreover, the invention can be reduced to an algorithm to determine the necessary scan resolution depending on the user""s desired amount of zoom and crop, the display medium and size, and perceived image quality. This algorithm could be used to warn the user of degraded image quality due to insufficient scan resolution or it could be used as a method for system design.